Letters of Intent received in 2016

LoI 2018-1934
Red giant stars as Galactic probes

Topics

- red giant structure
- transport processes
- stellar evolution
- stellar ages
- distances
- Galactic archeology
- red giants in clusters
- distances
- AGB

Rationale

Low-mass stars now benefit from new insights carried out by the thorough study of their oscillation spectra carried out by the space missions CoRoT and Kepler. Among them, red giants play a special role: they not only benefit from their bright magnitudes, so that plenty of light curves were recorded for seismology, but they also exhibit modes that directly probe their inner region, and especially their core. The space missions CoRoT and Kepler hence permitted to unravel the structure and evolution of low-mass red giant stars; K2, following Kepler, continues this task in various Galactic fields. The possibility of distinguishing between red giants burning helium in the core and those still only burning hydrogen in a shell has opened the way to strong physical outputs, complemented by the possibility to derive relevant estimates of the stellar masses and radii from the seismic scaling relations. Moreover, the measurement of the mean core rotation, often difficult for main-s equence stars but straightforward for subgiants and red giants, has revealed that significant transport of angular momentum must occur in the red giant interior.

Such a wealth of seismic information on red giants allows the development of a novel approach for investigating the Galactic stellar populations. For instance, the global seismic constraints can be used for inferring accurate distances, as well as estimates of red giant ages when coupled to modelling. All this information brings new lights for investigating stellar populations in the Milky Way.

This symposium is scheduled in autumn 2018 in order to timely benefit from the convergent studies of red giants carried out by many projects. By 2018, we shall have access to the 3rd release of Gaia data, which will contain distances, but also stellar parameters. Hence, Gaia will give constraints on two sides: strong constraints on stellar models, by the combined use of accurate distances and spectroscopy for a considerable number of stars; Galactic archeology, by analysis of the stellar age distribution in different regions of the Milky Way. Distances and stellar parameters delivered by Gaia will have to be compared to those derived from seismology completed by ground based spectrometry, verified for benchmark stars either bright enough for interferometric measurements of benefitting from interferometric measurement. This synergy of information of ageing stars will definitely strengthen our understanding of the physics and the evolution of red giants, and end up with the emergence of a chemodynamical investigation of the Galaxy.